US4689445A - Porcelain electrical insulator resistant to destruction by projectiles - Google Patents

Porcelain electrical insulator resistant to destruction by projectiles Download PDF

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Publication number
US4689445A
US4689445A US06/796,777 US79677785A US4689445A US 4689445 A US4689445 A US 4689445A US 79677785 A US79677785 A US 79677785A US 4689445 A US4689445 A US 4689445A
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Prior art keywords
shed
thickness
insulator
head portion
junction
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Expired - Lifetime
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US06/796,777
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English (en)
Inventor
Shoji Seike
Takao Totoki
Akio Kaneko
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NGK Insulators Ltd
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NGK Insulators Ltd
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Assigned to NGK INSULATORS, LTD. reassignment NGK INSULATORS, LTD. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: KANEKO, AKIO, SEIKE, SHOJI, TOTOKI, TAKAO
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B17/00—Insulators or insulating bodies characterised by their form
    • H01B17/02—Suspension insulators; Strain insulators

Definitions

  • the present invention relates to an electrical insulator. More specifically, the invention relates to an electrical insulator wherein when the insulator is impacted with a projectile and a shed is broken, a crack does not extend to a head portion thereof. Thus, for example, no reduction in power supply or line drop occurs.
  • Such an electrical insulator preferably consists essentially of alumina.
  • FIG. 10 An example of a heretofore known ceramics suspension insulator is shown in FIG. 10.
  • such an insulator has a thickness a of a head portion 51 which is to be covered with a cap approximately the same as the thickness b of a shed 52.
  • An object of the present invention is to obviate the aforesaid defects and to provide an electrical insulator having an excellent resistance to high speed projectiles such as a bullet from a gun.
  • the electrical insulator ameliorates the disadvantages of the above-mentioned insulators while maintaining sufficient electrical and mechanical integrity of the insulator. More particularly, the insulator is manufactured such that when the insulator is shot with a projectile, a possible crack does not extend to a head portion, resulting in the insulator being able to maintain sufficient mechanical and electrical characteristics.
  • an electrical insulator in which the thickness of the thinnest part of a shed is not less than 5 mm, and either the thickness of a head portion to be covered with a cap or the thickness in the vicinity of the junction portion between the head portion and the shed is not less than 2 times the minimum thickness of the shed.
  • the thickness of the insulator in the vicinity of the junction portion between the head portion and the shed is equal to the thickness from the tip of a projection between a pin hole into which a steel pin is to be inserted and fixed and the innermost recess portion to the external surface of the shed.
  • the electrical insulator in which the thickness of the insulator in the vicinity of the junction between the head portion and the shed is the thickness of the shed between the bottom portion of the innermost recess and the external surface of the shed.
  • the thickness of the insulator in the vicinity of the junction between the head portion and the shed is equal to the thickness of a projection between a pin hole in which a steel pin is to be inserted and fixed and the innermost recess.
  • the electrical insulator in which the length of ribs in the insulator are not less than 3 times the minimum thickness of the shed.
  • the electrical insulator which is made of an insulating material having an alumina content of not less than 40% by weight.
  • FIGS. 1, 2, 2A, 3 and 4 are partially sectional views of embodiments of the electrical insulators according to the present invention.
  • FIG. 5 is a schematic view illustrating a shooting test method carried out in the present invention.
  • FIG. 6 is a graph showing the relation between the content of alumina and amount of shed broken off in a high power projectile shooting
  • FIG. 7 is a graph showing the relation between the thickness of a shed and the puncture voltage of the shed according to the present invention.
  • FIG. 8 is a graph showing the relation between the thickness ratio thickness of a thickened part to a minimum thickness of the shed and the cracked rate of the head portions;
  • FIG. 9 is a graph showing the relation between the ratio of the height of a rib to the minimum thickness of the shed and the cracked rate of the head portions.
  • FIG. 10 is a partially sectional view showing a conventional electrical insulator.
  • 1, 11, 21, 31, 52 denote a shed, 2, 22 a tip of a projection, 3, 23 a pin hole, 4, 12, 24, 33 ribs, 5, 13, 25 a projection 6, 14, 27, 32, 51 a head portion, 7, 28 a recess, 15 a bottom portion of a recess, 26 a stepped portion, 41 a suspension insulator, 42 a ground surface, 43 a projectile orbit, and 44 a rifle.
  • the thickness of the insulator in the vicinity of the junction between the head portion and the shed denotes any one of the thickness from the tip end of a projection between a pin hole to which a steel pin is to be inserted and fixed and the innermost recess to the external surface of the shed, the thickness of the shed between the bottom portion of the innermost recess portion and the external surface of the shed, and the thickness of the projection between the pin hole into which the steel pin is to be inserted and fixed and the innermost recess portion.
  • the length of the outermost rib preferably the length of all the ribs, is not less than three times the minimum thickness of the shed, and the content of alumina is preferably in a range not less than 40% by weight.
  • the reason why the thickness of the head portion which is to be covered with a cap or the thickness of the insulator in the vicinity of the junction between the head portion and the shed is not less than 2 times the minimum thickness of the shed is that if the former is less than 2 times, a crack may extend to the head portion when the insulator is shot by a projectile. Consequently, the shot insulator cannot fully perform its function.
  • the length of the rib is not less than 3 times the minimum thickness of the shed and the content of alumina is not less than 40% by weight is that these parameters increase the mechanical strength of the insulator and reduce the rate at which cracks extend to the head portion.
  • an insulator which is free from cracking at the head portion, that is, free from a reduction in mechanical strength and a reduction of electrical characteristics of the head portion, can be obtained.
  • Ceramic raw materials shown by way of an example in Table 1, are prepared, and wet ground and mixed by means of a ball mill or the like, followed by filterpressing to obtain cakes.
  • the thus obtained cakes are extruded preferably by a de-airing extruder and molded into a desired shape.
  • the green body is molded into such a shape in which the minimum thickness of the shed and the thickness of the head or the vicinity of the junction between the head portion and the shed falls within the numerically limited ranges respectively, while the thickness of the shed and the length of the rib may be set at specific values.
  • the glazed body is fired in the temperature range from 1,250° to 1,450° C.
  • a cap is applied to the head portion of the fired insulator and a steel pin is secured into the pin hole by means of cement to assemble a suspension insulator.
  • FIGS. 1 through 4 are partially sectional views of embodiments of electrical insulators according to the present invention.
  • the minimum thickness t of the shed is 5 mm
  • FIG. 2 shows an embodiment in which the minimum thickness t of the shed 11 is 5 mm, the thickness of the insulator in the vicinity of the junction between the head portion 14 and the shed 11, that is, the thickness T of the thickened part from the bottom portion 15 of a recess between the projection 13 and the innermost rib 12 to the external surface of the shed 11 is 10 mm, and the length L of the outermost rib 12 is 25 mm.
  • FIG. 2A shows an embodiment similar to FIGS. 1 and 2, wherein the reference characters T, t and L have the same meaning as in the other Figures.
  • the numeral 61 denotes a shed portion
  • 62 represents a radially innermost rib
  • 63 represents a pin hole
  • 64 denotes a head portion
  • 65 is the thickened portion of the shed having a thickness T
  • 66 is the minimum thickness of the shed having a thickness t.
  • FIG. 3 shows an embodiment in which the minimum thickness t of the shed 21 is 15 mm, the thickness of the insulator in the vicinity of the junction between the head portion 27 and the shed 21, that is, the thickness T of the thickened part from the tip 22 of a projection 25 between the pin hole 23 and the recess 28 inside of the innermost rib 24 to a stepped portion 26 formed on the external surface of the shed 21 is 30 mm, and the length L of the outermost rib 24 is 45 mm.
  • FIG. 4 shows an embodiment in which the minimum thickness t of the shed is 15 mm, the thickness T of the head portion is 30 mm, and the length L of the outermost rib 33 is 30 mm.
  • FIG. 5 shows a schematic view of the shooting test
  • a suspension insulator 41 to be tested is upwardly set at a position 1 m above the ground surface 42 at an angle of 30° with respect to a projectile orbit 43.
  • a projectile is shot from a rifle 44 spaced 50 feet (about 15 m) from the suspension insulator 41 and at the same level as the insulator.
  • the projectile is directed to the bottom of a recess portion between the outermost rib and the outermost but one rib.
  • the projectiles used and gun used were 222 REM projectiles (projectile speed: 957 m/s, energy: 151 kg.m), a Savage 222 REM long, rifle gun model 340.
  • the cracked percentage of the head portion is a criterion for judging whether the insulator tested is to be unsuitable or not, depending upon the extension of cracks produced at the impact point and extending into the head portion, and is determined by the following equation through decomposing the shot insulator, the insulator being judged "to be unsuitable” whenever a crack extends to the head portion over the edge of the cap, and as "to be acceptable” whenever a crack does not extend to the head portion over the edge of the cap. ##EQU2##
  • suspension insulators according to the present invention having the respective profiles shown in FIGS. 1 to 4 and a suspension insulator having a conventional profile shown in FIG. 10 were prepared.
  • the above-mentioned shooting tests were carried out by using high power projectiles with respect to each of the thus prepared suspension insulators. Results are shown in Table 2, and the relation between the amount of shed broken off after the shooting test and the content of alumina is shown in FIG. 6.
  • x, ⁇ , and ⁇ denote "unsuitable”, “tolerable in actual application” although cracks are partially observed, and “no cracks", respectively.
  • the profile-improved suspension insulator according to the present invention in which the thin portion is formed in the shed, and the thickened portion is provided in the head portion or in the vicinity of the junction between the head portion and the shed, is extremely effective in that when the suspension insulator is shot by a high power gun, a crack does not extend to the head portion.
  • Suspension insulators which had the material in the composition range shown in Table 1 and the profile shown in FIG. 1 while the minimum thickness of the shed being varied in a range from 3 to 10 mm were prepared.
  • the puncture voltage of the shed was evaluated by using the thus obtained suspension insulators. This was done to determine the thickness level of the thinnest part of the shed which poses no practical problem, because abnormal high voltage may be applied onto the shed in a rare case such as lightning striking the actual line.
  • the evaluation of the minimum thickness of the shed under the high voltage is performed by the instantaneous application of a high voltage between the cap and the pin after assembly, and measuring the thickness at which an electric current is passed through the thinnest part of the shed.
  • FIG. 7 shows results thereof. As evident from the results of FIG.
  • the present invention is not limited to the above-mentioned Examples, and numerous modifications, variations and changes can be made.
  • the profiles of the insulator in the above Examples have been explained with respect to a suspension insulator.
  • the present invention can be favorably applied to other profile insulators, for instance, pin insulators.
  • the electrical insulators according to the present invention are provided with the thinnest part at the shed and with a thickened part in the head portion or in the vicinity of the junction between the head portion and the shed, cracks do not extend to the head portion of the insulator, for example, when the insulator is shot with a projectile.
  • insulators free from a reduction in mechanical strength and electrical characteristics can be obtained. Therefore, when the insulator is used in power transmission lines, even after being shot with a projectile, the mechanical strength and the electrical insulating properties of the insulator can be maintained, thereby preventing accidents such as line drop and power supply interruption.

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  • Insulating Bodies (AREA)
US06/796,777 1985-09-13 1985-11-12 Porcelain electrical insulator resistant to destruction by projectiles Expired - Lifetime US4689445A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP60-201836 1985-09-13
JP60201836A JPS6264010A (ja) 1985-09-13 1985-09-13 電気絶縁碍子

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US4689445A true US4689445A (en) 1987-08-25

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US (1) US4689445A (pt)
JP (1) JPS6264010A (pt)
CN (1) CN1007560B (pt)
AU (1) AU563020B2 (pt)
BR (1) BR8506009A (pt)
CA (1) CA1252163A (pt)
FR (1) FR2587535B1 (pt)
GB (1) GB2180701B (pt)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5147984A (en) * 1990-12-04 1992-09-15 Raychem Corporation Cap and pin insulator

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0785785B2 (ja) * 1991-08-21 1995-09-20 株式会社椿本チエイン 被塗物の回転搬送ラインにおける正立静止装置

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB213655A (en) * 1922-12-30 1924-03-31 Richard John Percival Briggs Improvements in or relating to insulators for supporting high-tension transmission cables and the like
GB296673A (en) * 1927-09-03 1929-11-07 Cie Generale Electro Ceramique Suspension insulators and strain insulators for electric conductors
US2383090A (en) * 1941-09-25 1945-08-21 Corning Glass Works Electric insulator
GB766230A (en) * 1955-03-21 1957-01-16 Albert Ag Chem Werke Improvements in or relating to electrical insulators
GB926544A (en) * 1960-01-20 1963-05-22 Asea Ab Electrical insulator for direct current transmission systems
US3141063A (en) * 1960-01-05 1964-07-14 Pilkington Brothers Ltd Toughened glass, pin type insulator
GB978501A (en) * 1962-11-08 1964-12-23 Siemens Ag An electrical insulator
GB1148977A (en) * 1966-05-20 1969-04-16 Cie Generale Electro Ceramique Improvements in pinned insulators

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE512395C (de) * 1927-04-01 1930-11-12 Steatit Magnesia Ag Vorrichtung zum Befestigen des Bolzens an Isolatoren mit Hilfe eines aus Draehten bestehenden ringfoermigen Druckkoerpers
FR1179477A (fr) * 1956-09-29 1959-05-25 Siemens Ag Procédé pour la fixation de la tige dans des isolateurs en verre à capot et tige
FR1278903A (fr) * 1961-01-19 1961-12-15 Asea Ab Isolateur spécial pour les transmissions d'énergie en courant continu
JPS53135493A (en) * 1977-04-28 1978-11-27 Ngk Insulators Ltd Cylindrical insulator
FR2445002A1 (fr) * 1978-12-21 1980-07-18 Ceraver Isolateur a dielectriques multiples

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB213655A (en) * 1922-12-30 1924-03-31 Richard John Percival Briggs Improvements in or relating to insulators for supporting high-tension transmission cables and the like
GB296673A (en) * 1927-09-03 1929-11-07 Cie Generale Electro Ceramique Suspension insulators and strain insulators for electric conductors
US2383090A (en) * 1941-09-25 1945-08-21 Corning Glass Works Electric insulator
GB766230A (en) * 1955-03-21 1957-01-16 Albert Ag Chem Werke Improvements in or relating to electrical insulators
US3141063A (en) * 1960-01-05 1964-07-14 Pilkington Brothers Ltd Toughened glass, pin type insulator
GB926544A (en) * 1960-01-20 1963-05-22 Asea Ab Electrical insulator for direct current transmission systems
GB978501A (en) * 1962-11-08 1964-12-23 Siemens Ag An electrical insulator
GB1148977A (en) * 1966-05-20 1969-04-16 Cie Generale Electro Ceramique Improvements in pinned insulators

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5147984A (en) * 1990-12-04 1992-09-15 Raychem Corporation Cap and pin insulator

Also Published As

Publication number Publication date
FR2587535A1 (fr) 1987-03-20
GB2180701A (en) 1987-04-01
CN1007560B (zh) 1990-04-11
GB2180701B (en) 1989-11-29
GB8529321D0 (en) 1986-01-02
JPS6264010A (ja) 1987-03-20
AU4976385A (en) 1987-03-19
CN85108664A (zh) 1987-03-11
FR2587535B1 (fr) 1989-03-24
CA1252163A (en) 1989-04-04
AU563020B2 (en) 1987-06-25
JPH0253887B2 (pt) 1990-11-20
BR8506009A (pt) 1987-06-16

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